Shock-timing experiments are indispensable to inertial confinement fusion mainly because the timing of multiple shock waves is crucial to understanding the processes of laser irradiation of targets.Investigations into shock waves driven by a two-step radiation pulse in polystyrene (CH) capsule targets are experimentally conducted at the ShenGuang Ⅲ laser facility.Differing from the traditional shock-timing implementation in which one shock wave could catch up with another one in solid CH,in this experiment,the second shock front in a rarefaction CH layer is observed through velocity interferometry.This second shock could also be made to converge with rarefaction waves within only a few micrometers of the CH capsule by designing the two-shock coalescence time.A shock-timing diagnostic technique to tune the multi-shock convergence in the CH capsule can thereby be achieved.The experimental results in the CH layer are quasi-quantitatively interpreted using streamlines simulated with the Multi-1D program.The experimental results are expected to offer important information for target structure and laser pulse design,both of which are important for realizing inertial confinement fusion.